Abstract
Staphylococcus aureus is an opportunistic bacterium that produces various types of toxins, resulting in serious food poisoning. Staphylococcal enterotoxins (SEs) are heat-stable and resistant to hydrolysis by digestive enzymes, representing a potential hazard for consumers worldwide. In the present study, we used amino-acid sequences encoding SEA and SEB-like to identify their respective template structure and build the three-dimensional (3-D) models using homology modeling method. Two natural compounds, Betulin and 28-Norolean-12-en-3-one, were selected for docking study on the basis of the criteria that they satisfied the Lipinski’s Rule-of-Five. A total of 14 and 13 amino-acid residues were present in the best binding site predicted in the SEA and SEB-like, respectively, using the Computer Atlas of Surface Topology of Proteins (CASTp). Among these residues, the docking study with natural compounds Betulin and 28-Norolean-12-en-3-one revealed that GLN43 and GLY227 in the binding site of the SEA, each formed a hydrogen-bond interaction with 28-Norolean-12-en-3-one; while GLY227 residue established a hydrogen bond with Betulin. In the case of SEB-like, the docking study demonstrated that ASN87 and TYR88 residues in its binding site formed hydrogen bonds with Betulin; whereas HIS59 in the binding site formed a hydrogen-bond interaction with 28-Norolean-12-en-3-one. Our results demonstrate that the toxic effects of these two SEs can be effectively treated with antitoxins like Betulin and 28-Norolean-12-en-3-one, which could provide an effective drug therapy for this pathogen.
Highlights
Staphylococcus aureus is among the most common microflora present on the skin and mucous membrane of humans and cattle [1]
The possession of virulence factors and survival of S. aureus in the host environment are attributed to the self-defense mechanism expressed by S. aureus that helps in protection against defense molecules produced by the host [5,6]
The present study extends our previous work to develop the 3-D model structure of the SEB-like that we identified from milk samples [21], and that of the SEA previously isolated from S. aureus Newman [22]
Summary
Staphylococcus aureus is among the most common microflora present on the skin and mucous membrane of humans and cattle [1]. In addition to its opportunistic pathogenicity, S. aureus is the most prevalent enterotoxin producing microbe that causes food-borne diseases among Staphylococcus species worldwide [4]. Staphylococcal enterotoxins (SEs) are responsible for major food poisoning outbreak with symptoms, such as violent vomiting, nausea and abdominal cramping with or without diarrhea [10,11,12,13]. In growth curve, these toxins are synthesized during the transition from logarithmic phase to the stationary phase, highly active even at low concentrations and resistant to heat as well as proteolytic enzymes [14,15]. We have carried out docking studies with the designated binding sites of the examined SEA and SEB-like using potent natural molecules Betulin and 28-Norolean-12-en-3-one
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